It is well known that the integrity of concrete structures is improved by insuring that the wet concrete poured into the form is substantially homogeneous; that is, with the aggregate spread and evenly distributed and all voids or air pockets being eliminated. To do this, it is common practice to insert a vibrating head into the wet concrete. As it is moved up and down and around the grid of reinforcing bars any pockets of aggregate are broken up and any voids or air bubbles are released and thus eliminated. A typical concrete vibrator includes an electric or gasoline motor connected through a flexible drive cable within a sheath to the vibrator head. The key to success in assuring the proper spreading of the aggregate and eliminating of the voids in the wet concrete is to provide an intense, reasonably high frequency and amplitude vibration of the head.
In the past, the typical approach is to provide an eccentric rotor mounted in the hollow casing to form the head. The rotor is usually formed by a simple machining process where one-half of a solid metal bar is removed. The curved segment formed by this machining process provides an imbalance so that upon rotation around the pintle shafts at the ends, the desired vibration is induced. Typically, the attempt to provide a more intense vibration, and thus provide for better aggregate spreading and void elimination, has been concentrated on providing different forms of motors to drive the rotor. The main objective of using different driving means is for the most part to simply increase the drive speed, and thus the vibration frequency.
A typical recent attempt is shown in the Lyle U.S. Pat. No. 4,057,222. The rotor is the standard one-half metal bar, as shown in FIG. 6, and the driving means is performed by a high speed hydraulic motor. In order to accomplish this increased speed, the vibrator of the '222 patent has thus evolved into a complicated and relatively expensive device to manufacture and to maintain operation.
In the past, it has been found that simply removal of one-half of the rotor leaves much to be desired in terms of the tendency of the rotor to flex laterally as it rotates at the increased speed necessary. One approach to try to overcome this problem is illustrated in the Oswald U.S. Pat. No. 5,108,189. As illustrated, an opposite side fin is left on the rotor during machining in an attempt to stiffen it (see FIGS. 1, 5 and 6). While this approach has some advantages, providing the fin and the curved segment that covers a full 180.degree. arc, as illustrated, means that a substantial portion of the overall mass, including the fin, does not provide any appreciable benefit to the vibrating action. As a point of reference, the centroid of the mass of the curved segment with the stabilizing fin, is positioned appreciably closer to the center of rotation, than in a mass without the fin, as proposed in the prior art '222 patent. Thus, while the design of the '189 patent may maintain increased rotor stability and strength to resist lateral flexing in the casing, the intensity of the vibration at a given rotating speed is significantly reduced.
Other attempts to improve the vibrating action have lead to complicating the structure of the rotor, even more than in the references mentioned above. Typical of these efforts is shown in the Lyle U.S. Pat. No. 4,428,678. As illustrated in this patent, the rotor itself it made up of numerous loose parts which inevitably provides for increased initial cost, as well as greater maintenance requirements.
More recently, some inventors have realized the shortcomings of complicating the structure of the rotor. This latest approach is simply to increase the size of the driving motor and use a speed enhancer to drive the rotor faster. While this does increase the vibration frequency, and thus to some degree the intensity, the cost of the unit is increased greatly, and of course the added cost and maintenance requirements is a significant negative factor. Typically, the driving speed for this type of concrete vibrator is in the range of 10,000-12,000 rpm. The engine required is typically a four cycle design, which adds additional cost to the unit. This more powerful engine is required in order to maintain sufficient torque to drive through the speed enhancer to reach the required high speed of the rotor. Furthermore, as illustrated in a typical approach of this type of arrangement, Breeding U.S. Pat. No. 5,829,874, the engine and speed enhancer unit becomes so heavy and bulky, that it must be adapted to being carried on a backpack for the worker. The lack of maneuverability and the fatigue factor for the worker using this type of concrete vibrator is unsatisfactory to most.
Therefore, it should be appreciated from reviewing the foregoing description of the known prior art, a need is identified for an improved concrete vibrator, particularly with respect to improving the efficiency of the vibration to provide better aggregate spreading and filling of the voids and air pockets, while at the same time providing such a vibrator that is lightweight and portable. Increasing the intensity of vibration at a more reasonable, reduced speed of rotation of the eccentric rotor can also be seen to be very desirable. In addition, the need exists for simplifying the unit to hold down the initial cost and to minimize maintenance requirements over the life of the unit. Overall, the concrete vibrator of the present invention should significantly enhance the ease and efficiency of use by the worker, to not only provide an increase in productivity, but to minimize fatigue.